Patent GB-1251799-A (GB)
Filed: 1967-11-23
Abstract: 1,251,799. Gas turbine engine fuel systems. JOSEPH LUCAS (INDUSTRIES) Ltd. Feb.11, 1969 [Nov.23, 1967], No.53359/67. Heading F1G. A fuel control system for a gas-fired gas turbine engine comprises a fuel gas valve including a valve control member movable to restrict gas flow from a fuel gas supply and a fuel-gasoperated servo-mechanism for positioning the valve control member, the servo-mechanism including a lever coacting with both the valve control member and with a pressure-sensitive element subjected to an air-pressure signal desired from the engine, and at least one pressure regulating means whereby a known proportion of the airpressure signal is supplied to the pressure-sensitive element. Fuel gas governed to a constant pressure by a valve 10 is supplied to burners of a gas turbine engine via a throttle valve 11 comprising a valve member 13 positioned by a piston 15 and a spring 22. The piston 15 is acted on by the pressure drop across an orifice 17 through which some of the fuel gas is bled via a passage 18 and a servo-valve 19, 20 to the downstream side of the valve 11. The valve 19, 20 is controlled by a lever 21 acted on by a diaphragm 26, the spring 22 and an opposing spring 24. The diaphragm 26 is acted upon on opposite sides by the discharge pressure P 2  of the engine compressor applied via a restrictor 30 and a passage 9, and the compressor intake pressure P o  applied via a restrictor 27. During acceleration, as the compressor discharge pressure increases, it acts by way of the diaphragm 26, lever 21 and servo-valve 19, 20 to increase the flow through the restrictor 17 and hence the force acting on the piston 15, whereby the valve 11 is progressively opened. During deceleration, the force exerted upon a stem 37 by a governor of a separate power turbine of the gas turbine engine decreases to allow the closure member 32 of a relief valve 31 to open wide against a stop 38. The pressure applied via the passage 9 to the diaphragm 26 then drops from the full compressor discharge pressure P 2  to a pressure intermediate the pressure P 2  and the intake pressure P o , as determined by the air potentiometer 30, 31. Overspeeding is prevented by a governor 39 driven by the engine and acting to restrict the flow through the passage 18 or to increase the flow through a by-pass passage (56), Fig. 2 (not shown), connected between the passage (9) and atmosphere. Compensation for variation of ambient temperature is provided by a temperature-sensing bulb (not shown) connected to a bellows 45 which acts on the governor 39 via a cam 44 and a spring 43. When starting the engine, a reduced fuel-flow is obtained by supplying gas at a controlled pressure via a restrictor 46 so that the pressure applied below the diaphragm 26 is increased from the value P o  to a value determined by the gas potentiometer 46, 27. Fig. 3 shows a modification in which the relief valve 31 is replaced by a relief valve 47 in which the valve member 50 is acted on by a diaphragm 48 in addition to the governor stem 37. The diaphragm 48 is subjected on opposite sides to the pressures P 2  and P o . A valve like the valve 47 may be used to control a pressure-sensitive valve in the passage 18.